Amyotrophic Lateral Sclerosis (ALS)

What Is ALS?

ALS is a disease that causes motor neurons, the nerve cells that send messages from your brain to your spinal cord and then to your muscles, to break down and die. These motor neurons control all your voluntary movements, allowing you to do things like walk, chew and swallow food, and even breathe.

There are two main types of these nerve cells. Upper motor neurons are located in the brain. They send signals down the spinal cord to the lower motor neurons, which tell the muscles to move.

With ALS, your brain can't send messages to your muscles anymore. Because the muscles don't get any signals, they become very weak and waste away. This is called atrophy. ALS is a progressive disease, which means it gets worse over time. As your muscles atrophy, it gets harder for you to walk, talk, eat, and breathe.

Types of ALS

There are two types of ALS:

Sporadic ALS is the most common form. It affects up to 95% of people with the disease. Sporadic means it happens sometimes without a clear cause.

Familial ALS (FALS) runs in families. About 5% to 10% of people with amyotrophic lateral sclerosis have this type. Changes to a gene cause FALS. Parents pass the faulty gene to their children. If one parent has the gene for ALS, each of their children will have a 50% chance of getting the gene and having the disease.

What Causes ALS?

Researchers still don't know exactly what causes amyotrophic lateral sclerosis. Gene changes, or mutations, are behind 5% to 10% of cases. Researchers have linked more than 12 mutations to the disease.

One mutation is to a gene that makes a protein called SOD1. This protein may be toxic to motor neurons. Other gene changes in ALS might also damage motor neurons.

The environment could also play a role in ALS. Scientists are studying whether people who come into contact with certain chemicals or germs are more likely to get the disease.

Scientists are also looking at these other possible causes:

Glutamate. This chemical is a type of neurotransmitter – it sends signals to and from the brain and nerves. With amyotrophic lateral sclerosis, glutamate builds up in the spaces around nerve cells and may damage them. The medication riluzole (Rilutek) works by lowering glutamate levels and can help make the disease progress more slowly.